Remote detection of concealed objects is an important task that arises in various activities. Remote detection of weapons and explosives is useful for combating terrorism by remotely detecting a suspect's hostile intent and safely isolating the armed suspect. Detection of humans or animals through obstacles is necessary for various rescue operations.
Remote monitoring of victim's psycho-physiological states may be an additional task during rescue operations. In many cases, remote monitoring allows timely aid for a patient when direct observation is impossible.
Prior art devices for remote surveillance, detection, and diagnostics utilize cameras operating in the visible or infrared spectrum. Such cameras are widely used for surveillance coverage of open spaces, buildings, and vehicles. However, such cameras deliver limited or no information when the target is concealed or obstructed by a barrier.
At security checkpoints, portal devices are often used to detect weapons and other dangerous items within the portal's inner zone. Portal devices have large dimensions and weight, thus are inappropriate for mobile use because they require the examined object to be positioned within the inner zone of the portal.
Prior art devices detect concealed objects using radar transponders that are configured to direct radar signals at a suspect and to detect a portion of the radar signals reflected by the suspect. A processor connected to the transponders processes the radar signals to determine whether the suspect carries a concealed object. When a concealed object is detected, a real-time alert such as an audible alert is produced.
Another type of object detection system detects a person entering a secured zone by illuminating the person with low-power polarized radio waves. Polarized waves in different direction are reflected back from the person. The return signals are collected and analyzed to determine that the person is hiding a weapon by calculating the difference of the reflected polarized signals in the time domain.